1. Field of the Invention
The present invention relates to a flat cable connecting structure, incorporated in a vehicle steering apparatus, for allowing electrical connection between a handle at a rotor side and a stator side.
2. Description of the Related Art
FIG. 8 is an exploded perspective view of a rotary connector. Such a rotary connector A generally comprises a set consisting of a upper cover 20 and a lower cover 21, linked concentrically so as to be rotatable relative to each other, a cable accommodating portion 22, and a flat cable 23 accommodated and wound in a space between the upper cover 20 and the cable accommodating portion 22 and the lower cover 21. Both ends of the flat cable 23 are electrically led out indirectly through an inwardly-bent lead block 24 and an outwardly-bent lead block 25 externally of the cable accommodating portion 22. Here, the inwardly-bent lead block 24 engages the outer edge of the upper cover 20, while the outwardly-bent lead block 25 engages the outer edge of the lower cover 21. In this case, since the upper and lower covers 20 and 21 have a circular outside shape, the inwardly-bent and outwardly-bent lead blocks 24 and 25 are formed into a shape which corresponds to this circular outside shape, so that they have either a recessed or protruding surface.
The upper cover 20 is formed as a movable element side housing, whereas a unit in which the lower cover 21 is integrally formed with the cable accommodating portion 22 is formed as a stationary element side housing. Clockwise or counterclockwise rotation of the movable element side housing causes the flat cable 23 to either wind or rewind in a space.
The rotary connector A generally having the above-described construction is used as an electrical connecting means to a vehicle air bag system, a horn circuit, or the like. In such a case, the stationary element side housing, composed of the lower cover 21 and the cable accommodating portion 22, is secured to a steering column of a steering device, the movable element side housing composed of the upper cover 20 is secured to the handle, and the two ends of the flat cable 23 are connected to the electrical parts at the steering column side and the handle side. Here, a known connecting structure for electrically leading out the flat cable is used. In the structure, conductor portions 23a and 23b at both ends of the flat cable 23 are connected to a connector 26 of another party, which is an electrical part disposed externally of the housings, through terminals 24a and 25a of the inwardly-bent lead block 24 and the outwardly-bent lead block 25, respectively, serving as external connecting parts.
A description will now be given of a conventional connecting structure, with reference to specific drawings. FIG. 5 is a perspective view showing a conventional connecting portion of a flat cable and an outwardly-bent lead block. FIG. 7 is a plan view of a conventional flat cable.
Referring to FIG. 5, the outwardly-bent lead block 1 is composed of a plurality of metal plates insert molded to a resinous molded part 2. One end of each metal plate protrudes from a side face of the resinous molded part 2, forming terminals 3, while the other ends of the metal plates are arranged in a substantially rectangular-shaped window 2a formed at about the center portion of the resinous molded part 2. These other ends of the metal plates form connecting terminals 4. In the conventional structure, six terminals 3 are used, four of which are disposed at the left side face of the resinous molded part 2 at equal intervals, and the remaining two being disposed at around the center portion of the side face. A cable holder 2b is provided at one end of the resinous molded part 2 in the longitudinal direction thereof, and is bent at two locations to form a bent surface 2b'. It is bent downwardly at about 45 degrees at one location, and virtually at right angles at the other location.
A pair of L-shaped first protrusions 2c and a pair of L-shaped second protrusions 2d are formed at around the center portion of the upper surface of the resinous molded part 2. The aforementioned window 2a in which the other ends of the metal plates are arranged is disposed between the first protrusions 2c and the second protrusions 2d. Parts of the metal plates exposed to the outside from the window 2a form the connecting terminals 4. Six connecting terminals 4, which is the same number as the number of terminals 3, are used, so as to allow connection in correspondence with the terminals 3 in an electrically conductive manner.
The flat cable 10 of FIG. 7 is composed of a pair of front and back films 11 and 12, and a plurality of conductors 13 embedded between the front and back films 11 and 12. The films 11 and 12 are each composed of a base film made of polyethylene terephthalate (hereinafter referred to as "PET") or the like, and are about 60 .mu.m thick. The conductors 13 are made of copper foil and are about 32 .mu.m thick. In the present embodiment, six conductors 13 are used to match the number of conductors 13 with the number of connecting terminals 4 of the outwardly-bent lead block 1. The arrangement pitch of the six conductors 13 is such as to match the arrangement pitch of the connecting terminals 4. The film 11 does not cover one end of the flat cable 10. The conductor portions 13a of the plurality of conductors 13 held by the back film 12, which is disposed where the front film 11 is not provided, is exposed to the outside. These exposed portions form conductor portions 13a.
In the longitudinal direction of the flat cable 10 from the conductor portions 13a, a pair of substantially square-shaped cutouts 14 that penetrate the side end surfaces of the front and back films 11 and 12 of the flat cable 10 are provided in the vicinity of the exposed conductor portions 13a. The cutouts 14 engage the second protrusions 2d of the outwardly-bent lead block 1 in order to place the flat cable 10 onto the cable holder 2b of the outwardly-bent lead block 1. Here, an end of the flat cable 10 is retained by the first protrusions 2c.
The conductor portions 13a, which are exposed portions at one end of the flat cable 10, oppose the connecting terminals 4 of the outwardly-bent lead block 1.
The conductor portions 13a of the flat cable 10 are connected to the connecting terminals 4 of the outwardly-bent lead block 1, using an ultrasonic welding machine (described later), and a connector 26, or the like, of another party (see FIG. 8) is connected to the terminals 3 of the outwardly-bent lead block 1, whereby the flat cable 10 is electrically led out to the outside.
As shown in FIG. 9, the ultrasonic welding machine comprises, for example, an anvil 30 for placing a work thereon, a horn 31 for ultrasonically vibrating the work in the direction of arrow A, and an air cylinder 32 for driving the horn 31 to apply pressure to the work in the direction of arrow B. A saw-toothed protrusion (not shown) is formed at an end of the horn 31 in correspondence with the pitch of the conductor portions 13a of the flat cable 10 Here, the conductor portions 13a and the connecting terminals 4 are workpieces. In ultrasonically welding the conductor portions 13a and the connecting terminals 4 together, the connecting terminals 4 of the outwardly-bent lead block 1 and the conductor portions 13a of the flat cable 10 are placed upon each other on the anvil 30. Then, as shown in the figure, when the protrusion of the horn 31 is used to ultrasonically vibrate the portion where the connecting terminals 4 and the conductor portions 13a are placed upon each other, while applying pressure thereto, solid-phase connection occurs between the connecting terminals 4 and the conductor portions 13a, whereby the plurality of connecting terminals 4 and the plurality of the conductor portions 13a are connected together at the same time.
FIG. 6 is a perspective view showing a conventional connecting portion of a flat cable and an inwardly-bent lead block. Referring to FIG. 6, the inwardly-bent lead block 5 is composed of a plurality of metal plates insert molded to a resinous molded part 6. The resinous molded part 6 includes a substantially square-shaped holder 6a for placing the flat cable 10 thereon; an inclined portion 6b, with a predetermined inclined surface, which extends from one end of the holder 6a in the longitudinal direction thereof; a terminal lead-out portion 6c extending from the bottom of a side face of the holder 6a; and a lead wire lead-out portion 6d extending at right angles from the lower right end of the terminal lead-out portion 6c.
A substantially rectangular window 6e is provided at the other end of the holder 6a, and a pair of L-shaped protrusions 6f are formed so as to protrude upwardly from the sides of the upper surface of the holder 6a. An end of each metal plate protrudes from a side face of the terminal lead-out portion 6c of the resinous molded part 6, thereby forming terminals 7 and lead wire connecting terminals 6g. The other ends of the metal plates are arranged in the window 6e of the resinous molded part 6, thereby forming connecting terminals 8. The lead wire connecting terminals 6g are formed in the lead wire lead-out portion 6d.
In the present embodiment, six connecting terminals 8 are used to be integrally connected to the four terminals 7 and the two lead wire connecting terminals 6g, respectively. The terminals 7 are connected, for example, to a horn circuit or a cruise control circuit through a connector 26' of the other part, and the lead wire connecting terminals 6g are directly welded or soldered onto lead wires (not shown), for electrical connection to an air bag system control circuit.
As mentioned above, the rotary connector A is constructed such that the movable element side housing formed by the upper cover 20 can rotate 2 to 2.5 times either clockwise or counterclockwise. However, at times, the movable element side housing formed by the upper cover 20 may be incorrectly mounted to the stationary element side housing composed of the lower cover 21 and the cable accommodating portion 22 so that the movable element side housing, for example, can rotate only once in either the clockwise or counterclockwise direction. Such an incorrectly assembled rotary connector A will be detected as a defective product, during inspection of the amount of rotation of the movable element side housing, using, for example, a torque meter, so that it cannot be shipped. Thus, the defective product must be thrown away.
This is because, when inspection of the amount of rotation is performed, and the movable element side housing is rotated to the terminal end upon one rotation, a pulling force, produced by rotation with a rotational torque greater than a predetermined value, is exerted onto the connecting portion of the conductor portions 13a of the flat cable 10 and the connecting terminals 4 of the outwardly-bent lead block 1. The pulling force on the connecting portion, first, acts upon the cutouts 14 of the flat cable 10, which engage the L-shaped second protrusions 2d of the outwardly-bent lead block 1.
The pulling force on the cutouts 14 causes partial deformation of the cutouts 14, or the cutouts 14 to disengage from the second protrusions 2d, and part of the pulling force is exerted onto the connecting portion of the conductor portions 13a and the connecting terminals 4.
The conductor portions 13a, made of thin copper foils as mentioned above, and the connecting terminals 4 are merely ultrasonically welded together at the connecting portion, so that the connecting portion cannot withstand the pulling force.
This may result in peeling of the connecting portion, so that the conductor portions and the connecting terminals are less reliably connected together. If the rotary connector A is constructed such that the movable element side housing is properly mounted to the stationary element side housing, and inspection for the amount of rotation is performed, the movable element side housing will ordinarily not rotate to the terminal end so as to exert a pulling force on the connecting portion. This is because when the movable element side housing of the rotary connector A, which is designed so as to be rotatable within a large enough rotational range of up to 2.5 revolutions either clockwise or counterclockwise, is secured to the handle of a vehicle, which can actually be rotated within a rotational range of up to two revolutions, the inspection results for the rotary connector will show that the inspection range of the rotary connector is up to two revolutions, so that the rotary connector will not rotate 2.5 times to the terminal end. Thus, when the movable element side housing is properly mounted to the stationary element side housing, part of the pulling force will not be applied to the connecting portion, with a rotational torque greater than a predetermined value, during shipment inspection.
When a pulling force is applied to the connecting portion of the conductor portions 13a and the connecting terminals 4 even once, the connecting portion may get peeled, thus reducing the reliability with which the conductor portions 13a and the terminals 4 are connected together. Thus, products, found to have unsuitable rotational ranges, during shipment inspection, had to be thrown away, instead of being adjusted.